Method for electrorefining crude copper having high antimony contents

ABSTRACT

A METHOD FOR ELECTROEFINING CRUDE COPPER INCLUDING ANTIMONY IN A HIGH CONCENUTRATION COMPRISING SUBJECTING THE CRUDE COPPER TO ELECTROLYSIS AS THE ANODE IN AN ELECTROLYTE CONTAINING SULFURIC ACID AND COPPER ION TO THUS DEPOSIT REFINED COPPER ON THE THIN COPPER CATHODE, WHEREIN THE ANODE AND THE CATHODE ARE CONNECTED TO A DRIECTCURRENT POWER UNIT PROVIDED WITH A POLARITY CONVERTING DEVICE AND DIRECT-CURRENT IS FED TO BOTH ELECTRODES OF SAID CATHODE AND SAID ANODE WHILE PERIODICALLY REVERSING THE DIREACTION OF THE CURRENT FLOW BETWEEN BOTH ELECTRODES AT SELECTED TIMES, WITH THE PROVISO THAT THE PERIOD OF TIME DURING WHICH POSITIVE POLARITY IS APPLIED TO THE ANODE IN EACH CYCLE OF THE TOTAL IMPRESSION CYCLES NECESSARY TO COMPLETE REFINEMENT OF THE VRUDE COPPER IS CONTROLLED IN THE RANGE OF NOT GREATER THAN 200 SECONDS AND THAT THE RATIO OF THE DURATIONS FOR IMPRESSION OF BOTH POLARITIES IS REGUALTED SO AS TO SATISFY THE FOLLOWING EQUATION: THE PERIOD OF TIME FOR IMPRESSION OF NEGATIVE POLARITY TO THE ANODE (SECONDS) PERIOD OF TIME FOR IMPRESSION OF POSITIVE POLARITY TO THE ANODE (SECONDS)=NOT LESS THAN 0.025. THE CRUDE COPPER INCLUDES FROM 0.1 TO 3.0 WT. PERCENT OF ANTIMONY AND AT LEAST 0.1 WT. PERCENT OF ARSENIC.

United States Patent Office 3,824,162 Patented July 16, 1974 3,824,162 METHOD FOR ELECTROREFINING CRUDE COP- PER HAVING HIGH ANTIMONY CONTENTS Kenichi Sakai and Morimasa Sumida, Takehara, Japan, assignors to Mitsui Mining & Smelting Co., Ltd.

No Drawing. Filed Oct. 24, 1972, Ser. No. 299,744 Claims priority, application Japan, Oct. 29, 1971, 46/85,534 Int. Cl. C22d 1/16 U.S. Cl. 204-108 6 Claims ABSTRACT F THE DISCLOSURE A method for electrorefining crude copper including antimony in a high concentration comprising subjecting the crude copper to electrolysis as the anode in an electrolyte containing sulfuric acid and copper ion to thus deposit refined copper on the thin copper cathode, wherein the anode and the cathode are connected to a directcurrent power unit provided with a polarity converting device and direct-current is fed to both electrodes of said cathode and said anode while periodically reversing the direction of the current flow between both electrodes at selected times, with the proviso that the period of time during which positive polarity is applied to the anode in each cycle of the total impression cycles necessary to complete refinement of the crude copper is controlled in the range of not greater than 200 seconds and that the ratio of the durations for impression of both polarities is regulated so as to satisfy the following equation:

the period of time for impression of negative polarity to the anode seconds)/ period of time for impression of positive polarity to the anode (seconds)==not less than 0.025.

The crude copper includes from 0.1 to 3.0 wt. percent of antimony and at least 0.1 wt. percent of arsenic.

BACKGROUND OF THE INVENTION (a) Field of the Invention The present invention relates to a method for electrorefining crude copper containing antimony and arsenic in high concentrations to thereby obtain copper of high purity.

(b) Description of the Prior Art Among the products from the smelting process of heavy metals, there are many kinds of copper-rich by-products containing antimony and arsenic in high concentrations as accompanying elements. And, among natural copper ores, there are ores containing antimony and arsenic in high concentrations along with copper. It has so far been very difiicult to obtain crude copper having a grade equivalent to one popular for use in electrorefining from these copper-containing by-products and copper ores, and to lower the contents of antimony and arsenic thereof so as to make it possible to employ same as the anode for use in electrorefining copper.

As for the contents of antimony and arsenic in particular among the impurities contained in the conventional anode for use in electrorefining copper, the former is in the range of 0.002 to 0.09% or thereabout and the latter is in the range of 0.0003 to 0.06% or thereabout.

In the case of crude copper obtained by smelting the foregoing copper-containing by-products and copper ores for the purpose of using them as the anode, however, antimony and/or arsenic remain therein to the extent of about 0.1% or more respectively. And, employment of an anode consisting of crude copper of such a grade in electrorefining would give rise considerably to suspended slime and to develop the so-called passive state of an anode, entailing suspension or stoppage of operation of the electrolysis.

SUMMARY OF THE INVENTION The present invention is intended to provide a method for electrorefining crude copper including antimony and arsenic in such high concentrations as above to thereby yield a high-purity copper efficiently.

The inventors of the present invention have electrolysed crude coppers including antimony and arsenic in high concentrations by applying various conditions for electrolysis and come to the findings as follows:

(a) When a crude copper including antimony and/or arsenic to the extent of about less: than 0.1% respectively is electrolysed by applying a current density of 150 to 180 amperes per square meter and under the condition of conventional electrolysis, there occurs no trouble even during a prolonged electrolysis. However, in case of a current density exceeding 200 amperes per square meter, no problems occur at the outset, but as the period of time for electrolysis exceeds 72 hours, a lot of suspended slime is generated to develop the so-called passive state of the anode and to bring about an abnormal voltage, whereby continuous operation of the electrolysis becomes dilficult.

(b) When a crude copper including antimony and arsenic in excess of 0.2% respectively is electrolysed, the higher is the content of antimony and arsenic and the higher is the current density applied to the electrolysis, the sooner there occurs an abnormal state of electrolysis (namely, passive state of anode) rendering it difiicult to continue the electrolysis.

And the occurrence of this abnormal state is more conspicuous in the case of a crude copper high in antimony content than in the case of crude copper high in arsenic content.

(c) When a crude copper including arsenic to the extent of 2% and antimony to the extent of less than 0.1%- is electrolysed by applying a current density of 150 to 200 amperes per square meter to the anode, there occurs no trouble. But, when a crude copper including antimony of 0.1% or more is electrolysed, the higher is the antimony content, the sooner is the occurrence of said abnormal state. For instance, in the case of effecting electrolysis by the use of a crude copper including 0.36% of antimony and 0.31% of arsenic while applying a current density of 150 amperes per square meter to the anode, there occurs an abnormal voltage in about to hours. In the case of electrolysis by applying the same current density as above and using a crude copper including 0.74% of antimony and 0.79% of arsenic, there occurs an abnormal voltage in about 90 hours, rendering it difiicult to continue the electrolysis any longer. When a similar crude copper including about 0.7% of antimony is electrolysed by applying a current density of 220 amperes per square meter, electrolysis becomes difiicult 35 to 40 hours after the start of operation. And, in the case of a crude copper including about 1.6% of antimony, it becomes impossible to continue the electrolysis 10 to 15 hours after the start of operation.

As is evident from the foregoing, according to the conventional electrolysis to be operated by applying a current density in the range of 200 to 250 amperes per square meter, electrolytic treatment of crude copper including 0.1% or more of antimony is difficult, and therefore, there has been a need for development of an eifective method of treating crude copper of this sort.

(d) When a crude copper having the above composition which gives rise to an abnormal state in the course of electrolysis rendering it ditficult to continue the electrolysis is subjected to electrorefining as the anode, break of the electric current for electrolysis for a short time or temporary reversal of the direction of current flow can dispel said abnormal state and renders it possible to continue the electrolysis.

The present invention has been accomplished on the basis of the foregoing findings obtained through electrolysis of crude coppers including 0.1% or more of arsenic and antimony in a high concentration under various conditions of electrolysis.

To be precise, the present invention relates to a method for electrorefining crude copper, which features a clever application of the process for a plating method known as the electroplating method of periodic reversal current to an electrorefining of those crude coppers of high antimony contents which have hitherto been considered to be difiicult or impossible to electrolyse by the known electrore'fining methods. That is, the process of making electric current flow in reverse directions at regular intervals, thereby efficiently producing a high-purity copper having a grade equal to that of the conventional electrolytic copper from said crude coppers through electrorefining.

At the time of etfe'cting electrolysis by employing a crude copper including antimony and arsenic in high concentrations as the anode, it is desirable to set both the period of time for regular flow of electric current and the period of time for reverse flow of electric current to be short, and it is preferable to set the ratio of the period of time for reverse flow of electric current '(seconds) to the period of time for regular flow of electric current (seconds) to be as small as possible. In this context, said regular flow of electric current means the case of applying an electric current by employing an electrode consisting of crude copper as the anode, that is, the case of impressing positive polarity on said electrode consisting of crude copper, while said reverse flow of electric current means the case of applying an electric current by employing an electrode consisting of crude copper as the cathode, that "is, the case of impressing negative polarity on said electrode consisting of crude copper. For instance, in the case of electrorefining employing a crude copper including at least 0. 1% of antimony and at least 0.-l% of arsenic as the anode and effected by applying a current density of 200 to 400 amperes per square meter and various ratios of the period of time for reverse flow of electric current to the period of time for regular flow of electric current, that is, when the period of time for reverse flow of electric current is set in the range of from 1 second to about l seconds while the corresponding period of time for regular flow of electric current is set in therange of from about 10 seconds to about 300 seconds so as to apply various ratios of the reverse flow of current to the regular tflow of current ranging lfI'Olll to V at the time of applying electric current, there are observed such tendencies as shown in (a) to (d) below:

(a) When the ratio of the duration of reverse current flow to the duration of regular current flow is less than =0.025), regardless of the length of said durations, recovery from the abnormal state of electrolysis tends to be slow.-

'(b) Even when the ratio of the duration of reverse current flow to the duration of regular current flow is fixed at 0.025 or more, in case the duration of the regular current flow is set to be long, say, at a value exceeding 180 seconds, generation of the suspended slime tends to increase in a way, leading to a slow recovery from the abnormal state of electrolysis. Therefore, it is desirable to set said duration to be not greater than 200 seconds.

*(c) [Even when the duration of the reverse current flow is set at a value considerably exceeding 1 second, the effect of recovery from the abnormal state of electrolysis is not necessarily enhanced in proportion to the increase in said value. Therefore, it is also obviously desirable to set it to be usually not more than 1 second from the viewpoint of current efliciency too. And, with a view to satisfying the aforesaid ratio of 0.025, when the duration of the regular current flow is set to be 200 seconds for instance, the duration of the reverse current flow is required to be at least 5 seconds for complete recovery from the abnormal state of electrolysis, and when the duration of the regular current flow is set to be 10- seconds, the duration of the reverse current flow is required to be at least 0.25 second for the same purpose.

(d) In the case of a crude copper including antimony in the range of [from 0.1% to less than 0.4% in concentration, which has been considered unsuitable for a long spell of electrolysis by the conventional methods (which apply a current density of 200 to 250 amperes per square meter), the method of the present invention renders it possible to continue a normal operation of electrolysis for a long period of time even at as high a current density as 350 amperes per square meter. However, it becomes somehow difficult to continue the normal operation at the current density of 400 amperes per square meter. And, in the case of a crude copper including antimony of 0.4% or more in concentration, a long spell of electrolysis can be satisfactorily operated at a current density of 200 to 250 amperes per square meter, while in the case of a crude copper including antimony exceeding 3%, restoration of the normal state of electrolysis and operation ot a long spell of electrolysis become obviously difiicult.

Though the arsenic content in a crude copper usually approximates the antimony content therein, it does not restrict the conditions of electrolysis so much as antimony in the operation of electrolysis under the foregoing various conditions. However, a crude copper including more than 3% of arsenic tends to lower the grade of products, and, therefore, it is desirable to use a crude copper including less than 3%, preferably less than 2%, of arsenic to be subjected to treatment by the method of the present invention.

In view of the foregoing tendencies, on the occasion of practicing the electrorefining of crude copper as the anode according to the method of the present invention, it is most appropriate to employ a rectifier capable of converting the polarity from positive to negative and vice versa, to set the ratio of the duration of the reverse current flow (seconds) to the duration of the regular current flow (seconds) at more than 4 preferably in the range of A to A and, in the case of the anode consisting of a crude copper including arsenic of not less than 0.1% and antimony in the range of from 0.1% to less than 0.4%, to set the duration of the reverse current flow preferably at less than 10 seconds, more preferably less than 5 seconds, while setting the duration of the regular current flow preferably at less than 200 seconds, and applying a current density of less than 400 amperes per square meter. When a crude copper including arsenic of not less than 0.1% and antimony in the range of from 0.4% to 3% is used as the anode, it is most appropriate to operate the electrolysis by setting the duration of the regular current flow at 200 seconds or less in fixing the aforesaid ratio of durations of current flows and by applying the regular current flow and the reverse current flow alternately at a current density of not greater than 250 amperes per square meter. As for the lower limit of the current density in this connection, in case the current density applied is less than amperes per square meter, it would nullify the advantage of application of the method of the present invention, so that it is usual to adopt 150 amperes per square meter as the lower limit of current density.

As for the temperature of the electrolyte at the time of electrolysis according to the present invention, the higher it is, the more it is efiective for preventing the occurrence of the abnormal state of electrolysis, and yet, in case it is more than about 65 C., there would occur roughdeposit on the surface of the produced electrolytic copper. For this reason, it is desirable to hold the temperature of the electrolyte at the time of electrolysis according to the method of the present invention in the range of about 55 to 65 C. The present invention is, as set forth above, a method capable of displaying an excellent effect in electrorefining of crude coppers including antimony and arsenic in high concentrations, a method capable of producing electrolytic copper in high efliciency particularly in the case of a crude copper including antimony of, say, less than 0.4% at as high a current density as 350 amperes per square meter. But, when the content of antimony is especially high such as exceeding 1%, the grade of the resulting product electrolytic copper tends to be somewhat inferior to that obtained from a crude copper including less than 1% of antimony. Consequently, when the quality of the product is taken into consideration, a crude copper including less than 0.6% of antimony is most suitable to be treated by the method of the present invention.

In the present invention, the distance between the crudecopper electrode (or anode) and the pure-copper electrode (or cathode) in an electrolytic cell is desirable to be maintained in the range of about 100 to 120 mm. And, the feeding of the electrolyte to the electrolytic cell in the present invention is operated in such a fashion that the electrolyte is put in said electrolytic cell through one end of the cell and discharged through the opposite end thereof for recycling. In this context, it is advisable to provide a filter for the electrolyte-cycling channel outside the electrolytic cell so as to remove the colloidal matters in the discharged electrolyte arising from electrolysis. Besides, addition of a small quantity of the powder of an appropriate filtering assistant such as diatomaceous earth to the electrolyte to be filtered has the effect of not only keeping the function of the filter in good order for hours but also imparting fine appearance to the refined copper.

In the present invention, the conditions for electrolysis other than those described in the foregoing are much the same as those for the conventional electrolysis, and yet, it is desirable that, in the electrolyte for use in the present invention, the concentration of Cut+ ion is in the range of about 40 to 50 g./l., the concentration of H 80 is in the range of about 170 to 210 g./l., and it is further advisable to add glue to the extent of from about 4 to 100 g./ton electrolytic copper and thiourea to the extent of from about 50 to 150 g./ton electrolytic copper to said electrolyte. As for Clion, it is appropriate to make its concentration in said electrolyte be less than 0.1 g./l.

According to the present invention as described above, it is possible to obtain in high efiiciency an electrolytic copper containing more than 99.99% of copper, less than 0.0002% of antimony and less than 0.0002% of arsenic.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereunder will be a further elucidation of the present invention by reference to some embodiments thereof.

Example 1 Electrorefining was conducted by the use of a crude copper including 97.13% by weight of copper, 0.6% by weight of antimony and 1.6% by weight of arsenic as the anode. The electrolyte composed of 40 g./l. of copper and 200 g./l. of sulfuric acid (in concentration) was fed to the electrolytic cell by cycling at the rate of 18 to 20 l./min. while its temperature being held at 59 to 61 C. When the electrolysis was effected by applying a current density of 200 to 220 amperes per square meter, there occurred an abnormal state about 45 hours after the start of electrolysis, whereby electrolytic dissolution of the anode became difficult and continuous operation of the electrolysis became impossible. At this juncture, the electrolysis Was switched over to the method of the present invention. That is, upon setting the duration of the regular current flow to be 90 seconds and the duration of the reverse current fiow to be 3 seconds by means a polarity converter (a manufacture of Hirao Denki K.K.), electric current was flowed in opposite directions alternately. As a result, it became possible to perform the electrolysis very easily.

Example 2 When electrolysis was conducted by the use of a crude copper including 95.84% by weight of copper, 0.7% by weight of antimony and 2.6% by weight of arsenic as the anode and under the conditions for electrolysis of 220 am peres per square meter in current density, 59 to 61 C. in temperature of electrolyte, 100 mm. in electrodes distance, 18 to 20 l./min. in cycling rate of electrolyte, use of electrolyte consisting of 40 to 43 g./l. of copper, 190 to 200 g./l. of sulfuric acid, 0.2 g../l. of antimony and 1.3 g./l. of arsenic, duration of regular current flow set at seconds, and duration of reverse current flow set at 3 seconds, normal operation of the electrolysis was possible. The cell voltage for electrolysis in this case was 0.28 v. in the early stage and 0.28 v. at the end. The current efiiciency was 99.3% for the regular current fiow and 93.0% for the total current flow. The impurities among the deposited substances were more than 0.0001% of antimony and 0.0002% of arsenic.

Example 3 When electrolysis was conducted by the use of a crude copper including 93.64% by weight of copper, 2.1% by weight of antimony and 3.4% by weight of arsenic as the anode and under the conditions for electrolysis of 220 amperes per square meter in current density, 59 to 61 C. in temperature of electrolyte, mm. in electrodes distance, 18 to 20 l./min. in cycling rate of electrolyte, use of electrolyte consisting of 40 to 43 g./l. of copper, 190 to 200 g./l. of sulfuric acid, 0.2 g./l. of antimony and 1.3 g./l. of arsenic, duration of regular current flow set at 180 seconds, and duration of reverse current flow set at 9 seconds, normal operation of the electrolysis was possible. The current efiiciency was 99.5% for the regular current flow and 89.6% for the total current flow. The impurities among the deposited substances were 0.0014% of antimony and 0.007% of arsenic.

Example 4 As a result of continuous operation of electrolysis for about 2 months, using crude copper having copper content in the range of 99.0 to 99.2%, antimony content in the range of 0.1 to 0.19% and arsenic content in the range of 0.05 to 0.15% as the anode, under the conditions of 350 amperes per square meter in current density, 62 to 65 C. in temperature of electrolyte, 100 mm. in electrodes distance, 15 to 20 l./min. in cycling rate of electrolyte, use of electrolyte consisting of 38 to 42 g./l. of copper, 183 to 187 g./l. of H 80 0.01 to 0.037 g./l. of Cl and 0.3 g./l. of antimony, filtration of electrolyte in its entirety, alternate application of regular current flow which duration was set at 16 seconds and reverse current flow which duration was set at 1 second, the state of electrodeposition was satisfactory and the voltage of unit cell showed no abnormality. The concentration of antimony in the electrolyte which had been 0.35 g./l. at the beginning attained a maximum of 0.55 g../l.

The electrolytic copper obtained through this electrolysis contained less than 0.0001% of antimony and less than 0.0001% of arsenic. And, the current etficiency was 95.0% for the regular current flow and 86% for the total current fiow.

What is claimed is:

1. A process for the electrolytic refining of crude copper, which comprises subjecting to electrolysis a first electrode of crude copper containing from 0.1 to less than 0.4 Wt. percent of antimony and at leastO.1 wt. percent of arsenic to deposit purified copper onto a second electrode, employing as the electrolyte an aqueous solution containing sulfuric acid and copper ions and maintaining the temperature of the electrolyte in the range of about 55 to 65 C. during the electrolysis, the electrolysis being carried out by flowing a DC. current, at a current density of from to 400 a./m. between said electrodes with positive polarity being applied to said first electrode for a period of time of less than 200 seconds, followed by reversing the polarities of said electrodes for a period of time such that the following equation is satisfied time of applying negative polarity to first electrode time of applying positive polarity to first electrode and then repeating the cycle until the purified copper is deposited on the second electrode.

2. A process according to Claim 1, in which the positive polarity is applied to said first electrodefor at least 10 seconds.

3. The electrolytic refining process according to Claim 1, wherein the crude copper includes arsenic in the range of from 0.1 to 3% by weight.

4. A process for the electrolytic refining of crude copper, which comprises subjecting to electrolysis a first electrode of crude copper containing from 0.4 to 3.0 wt. percent of antimony and at least 0.1 Wt. percent of arsenic to deposit purified copper onto a second electrode, employing as the electrolyte an aqueous solution containing sulfuric acid and copper ions and maintaining the temperature of the electrolyte in the range of about 55 to 65 C. during the electrolysis, the electrolysis being carried out by flowing a DC current, at a current density of from 150 to 250 a./m. between said electrodes with positive polarity being applied to said first electrode for a period of time of less than 200 seconds, followed by reversing the polarities of v said electrodes fora period of time such that the following equation is satisfied. time of applying negative polarity to first electrode time'of applying positive polarity to first electrode and then repeating the cycle until the purified copper is deposited on the second electrode. f v

'5. A process according to Claim4, in which the positive polarity is applied to 'said'first electrode for at least lseconds. j n L j,

6. The electrolytic refiningprocess according to Claim 4, wherein the crude copper contains arsenic in the range of from 0.1 to 3% by weight.

References Cited UNITED STATES PATENTS 10/1972 Schulze 204-108 3,755,111 8/1973 Lindstrom 204-108 FOREIGN PATENTS 1,157,686 7/1969 -Great Britain 204-106 HOWARD s. WILLIAMS,.Primary Examiner W. I. SOLOMON, Assistant Examiner US. Cl. X.R.

204-106, 293, Dig. 8, Dig. 9 

